[IPV6] ip6_tunnel: release cached dst on change of tunnel params

The included patch fixes ip6_tunnel to release the cached dst entry
when the tunnel parameters (such as tunnel endpoints) are changed so
they are used immediatly for the next encapsulated packets.
Signed-off-by: Hugo Santos <hsantos@av.it.pt>
Acked-by: Ville Nuorvala <vnuorval@tcs.hut.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_tunnel.c

@@ -884,6 +884,7 @@ ip6ip6_tnl_change(struct ip6_tnl *t, struct ip6_tnl_parm *p)
 	t->parms.encap_limit = p->encap_limit;
 	t->parms.flowinfo = p->flowinfo;
 	t->parms.link = p->link;
+	ip6_tnl_dst_reset(t);
 	ip6ip6_tnl_link_config(t);
 	return 0;
 }